JPH0370849A - Exhaust air purifying device of internal combustion engine - Google Patents

Abstract

PURPOSE:To obtain a regularly stable exhaust purifying efficiency by providing, in the lower stream of a catalytic converter rhodium, a diagnostic sensor having two detecting elements for outputting electromotive forces according to oxygen concentration, with either of the elements having a nitrogen oxide reducing catalyst layer so that it can also sense the oxygen in nitrogen oxide. CONSTITUTION:A nitrogen oxide reducing catalyst layer is provided only on either of two oxygen concentration detecting elements of a diagnostic sensor (e) so that it can also sense the oxygen in nitrogen oxide. Thus, according to an increase in nitrogen oxide in the exhaust air, a difference is caused in the electromotive forces outputted from the two detecting elements of the diagnostic sensor (e). An abnormality detecting means (f) detects abnormality of nitrogen oxide exhaust quantity by this difference of the electromotive forces. When the abnormality is detected, the exhaust reflux quantity by an exhaust reflux control means (d) is increased and changed. Namely, when the nitrogen oxide in the exhaust air in the lower stream of a catalytic converter rhodium is increased, the exhaust reflux quantity is increased to reduce the combustion temperature, whereby the reduction effect of nitrogen oxide by exhaust reflux is stably ensured.

Description

[Detailed description of the invention] <Industrial application field> The present invention relates to an exhaust gas purification device for an internal combustion engine.

<Prior Art> Conventional exhaust gas purification devices include the following.

That is, it has become common to have a three-way catalyst installed in the exhaust passage that oxidizes CO and HC in the exhaust gas and reduces and purifies NOx.

The conversion efficiency (purification efficiency) of this three-way catalyst is set so that it functions effectively under the exhaust conditions during combustion at the stoichiometric air-fuel ratio.

Therefore, during normal operation other than during high-load operation where particularly high output is required, the air-fuel ratio is detected by detecting the oxygen concentration in the exhaust with an air-fuel ratio sensor installed in the exhaust passage upstream of the three-way catalyst. Generally, the air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio.

As an example of the above air-fuel ratio sensor, Japanese Patent Application Laid-open No. 58-2043
There are some as shown in Publication No. 65 and the like.

The electromotive force of this air-fuel ratio sensor has a characteristic that it changes suddenly near the stoichiometric air-fuel ratio, and by comparing this electromotive force with a reference voltage (slice level), the air-fuel ratio of the air-fuel mixture is compared to the stoichiometric air-fuel ratio. Determine whether it is rich or not.

For example, when the air-fuel ratio is lean (rich), the air-fuel ratio is controlled to be close to the stoichiometric air-fuel ratio by increasing (reducing) the fuel injection amount Ti.

In this way, the three-way catalyst is adjusted to function effectively.

However, air-fuel ratio control using such an air-fuel ratio sensor has caused the following problems.

In other words, the oxygen in NOx should originally be detected as the oxygen concentration in the exhaust gas, but this air-fuel ratio sensor cannot detect this, so the higher the NOx concentration, the lower the true stoichiometric air-fuel ratio. The electromotive force is reversed on the lean side, thereby controlling the air-fuel ratio to the lean side.

In this way, if the control point (reversal point) is shifted to the lean side and the air-fuel ratio is controlled to be lean, fuel efficiency can be improved to a certain extent, so it is actually an advantageous control.
Under operating conditions (high combustion temperature conditions) where NOx increases due to high rotation and high load, the NOx reduction function of the three-way catalyst is impaired and NOx
The amount generated will increase significantly.

Therefore, during high-load operation when the combustion temperature rises and the amount of NOx emissions increases, part of the exhaust gas is returned to the intake passage.
By lowering the combustion temperature, the amount of NOx emissions is reduced.

In this case, an exhaust gas recirculation passage is formed that communicates from the exhaust passage to the intake passage, and a control valve is provided in the middle of this passage to control the amount of exhaust gas recirculation depending on the engine operating state.

<Problems to be Solved by the Invention> However, although exhaust gas recirculation utilizes the negative pressure in the intake passage, there are problems such as changes in atmospheric pressure due to altitude, changes in combustion pressure, and the orifice of the exhaust recirculation passage. There was a problem in that the amount of exhaust gas recirculation changed due to deterioration, making stable control of NOx impossible.

SUMMARY OF THE INVENTION In view of these conventional problems, it is an object of the present invention to provide an exhaust gas purification device that can always obtain stable exhaust gas purification efficiency.

Means for Solving the Problems> In order to achieve the above object, the present invention, as shown in FIG. An exhaust gas recirculation passage (b) that recirculates part of the exhaust gas to the intake passage; a control valve (C) that is interposed in the exhaust gas recirculation passage and controls the amount of exhaust gas recirculation; and a control valve (C) that controls the amount of exhaust gas recirculation based on the operating state of the engine. Exhaust recirculation amount control means (d
), and an exhaust gas purification device comprising two detection elements downstream of the three-way catalyst that are sensitive to oxygen and output an electromotive force according to the oxygen concentration, and only one of which detects nitrogen oxide reduction. A diagnostic sensor (e) is provided with a catalyst layer so that it can also be sensitive to oxygen in nitrogen oxides, and the amount of nitrogen oxides discharged can be determined based on the difference in electromotive force between the two detection elements. an abnormality detecting means (f) for detecting an abnormality; and a changing means (8) for increasing or changing the amount of exhaust gas recirculated by the exhaust gas recirculation amount control means when the abnormality is detected by the abnormality detecting means.
The configuration includes: and .

<Function> In the above configuration, only one of the two detection elements of the diagnostic sensor is provided with a nitrogen oxide reduction catalyst layer so that it can also be sensitive to oxygen in nitrogen oxides. As nitrogen oxides increase, a difference arises in the electromotive voltages output from the two detection elements of the diagnostic sensor.

Therefore, the abnormality detection means detects an abnormality in the amount of nitrogen oxide discharged based on the difference in electromotive voltage.

When an abnormality is detected, the exhaust gas recirculation amount by the exhaust gas recirculation control means is increased or changed.

In other words, when nitrogen oxides increase in the exhaust gas downstream of the three-way catalyst, the amount of exhaust gas recirculation is increased and the fuel temperature is lowered, thereby lowering the concentration of nitrogen oxides in the exhaust gas. Efforts are made to ensure a stable oxide reduction effect.

<Example> Examples of the present invention will be described below based on FIGS. 2 to 9.

Referring to FIG. 2, a system according to an embodiment of the present invention will be described.

The intake passage 22 of the internal combustion engine 21 is provided with an air flow meter 23 that detects the intake air flow rate Q and a throttle valve 24 that controls the intake air flow rate Q in conjunction with the accelerator pedal. An electromagnetic fuel injection valve 25 is provided.

The fuel injection valve 25 is driven to open by an injection pulse signal from a control unit 26 having a built-in microcomputer, and injects fuel that is pressure-fed from a fuel pump (not shown) and controlled to a predetermined pressure by a pressure regulator.

Further, an air-fuel ratio sensor 29 is provided in the exhaust passage 28, and further downstream a three-way catalyst 30 is provided that purifies the exhaust gas by oxidizing Co and HC and reducing NOx.

Further, an exhaust gas recirculation passage 31 is formed which communicates with the intake passage 22 downstream of the throttle valve 24 from the exhaust passage 2B, so that a portion of the exhaust gas is recirculated.

A control valve 32 for controlling the amount of exhaust gas recirculation is interposed in the middle of the exhaust gas recirculation passage 31.

The amount of exhaust gas recirculation is determined by the engine speed N, which is a parameter of the engine operating state, and the basic fuel injection amount Tp (= to -Q/N; K
is a constant), the exhaust gas recirculation amount according to the operating state at that time is determined by the controller/LzLnint 26 from a map set in advance, and the control valve 32 is controlled by the control unit 26, and the control valve 32 is controlled by its opening degree. Ru.

Further, downstream of the three-way catalyst 30, a diagnostic sensor 1, which will be described later, is installed.
1 is provided, and its output is input to the control unit 26.

Further, the distributor (not shown) has a built-in crank angle sensor 33, and the crank angle unit angle signal outputted from the crank angle sensor 33 in synchronization with engine rotation is counted for a certain period of time, or the crank angle reference angle is The engine rotation speed N is detected by measuring the period of the signal.

The configuration of the diagnostic sensor 11 will be explained with reference to FIGS. 3 and 4.

A first detection element 12 and a second detection element 13 are attached to the diagnostic sensor 11 with a predetermined gap between them by an insulating member 14 made of alumina or the like.

Each detection element 12.13 includes, for example, zirconium oxide (
Solid electrolyte members 12A, 13 whose main component is ZrO2)
Hollow air introduction chambers 12B, 13B are formed by A, and first and second inner electrodes 15A, 16A facing these air introduction chambers 12B, 13B, and solid electrolyte members 12A, 13A are attached to these inner electrodes 15A, 16A. first and second outer electrodes 15 facing each other and in contact with the exhaust gas;
B, 16B are formed. These electrodes are made of platinum (
Pt).

The first and second outer electrodes 15B, 16B are covered by first and second electrode protection N17.18.

Here, the first outer electrode 15B on the first detection element 12 side
The first electrode protection [17] covers, for example, rhodium (Rh) on a carrier made of porous ceramic such as gamma alkoxide (T-A1203), titanium oxide (Ti02), lanthanum oxide (LazO:+), etc.

It is formed to have a NOx reduction function by mixing particles of at least one catalyst such as ruthenium (Ru) that promotes the NOx reduction reaction.

On the other hand, the second electrode protection 118 that covers the second outer electrode 16B of the 13 second detection elements is formed of a magnesium spinel layer.

Then, an electromotive force (1) generated between the inner electrode 15A and the first outer electrode 15B of the 12 first detection elements, and the second inner electrode 16A and the second outer electrode 16B of the 13 second detection elements. The electromotive voltage V2 generated between the two is independently taken out and input to the control unit 26.

In the diagnostic sensor 11 having such a structure, the electromotive force characteristic generated between the first inner electrode 15A and the first outer electrode 15B of the first detection element 12 is as shown by the solid line in FIG. Due to the NOx reduction action of the NOx reduction catalyst particles in the protective layer 17, oxygen in NOx is also well detected as a variation in oxygen concentration in the exhaust gas, and even when NOx increases, the characteristic is that the air-fuel ratio suddenly changes at a point close to the stoichiometric air-fuel ratio. In other words, the average electromotive voltage has a constant value regardless of Noxt.

On the other hand, the electromotive voltage characteristic generated between the second inner electrode 16A and the second outer electrode 16B of the second detection element 13 is as shown by the dotted line in FIG. Not detected as NOx? The point where the electromotive force suddenly changes as the temperature increases is a characteristic that shifts to the lean side when there is a lot of NOx. In other words, the more NOx there is, the higher the average electromotive voltage becomes.

Furthermore, in detail, when the operating condition is normal, there is no N in the exhaust gas.
When Ox is low, as shown in FIG. 6, the average electromotive voltage from the first detection element 12 and second detection element 13 of the diagnostic sensor 11 are both stable around 0.5V, but as shown in FIG. As shown in FIG. 2, when the load is high and the operating state is such that NOx increases, the first detection element 12 can detect oxygen in NOx as oxygen in the exhaust gas, so there is no change in the average electromotive force, but the first detection element 12 Since the second detection element 13 cannot detect oxygen in NOx, the average electromotive voltage increases accordingly, and finally,
The electromotive voltage V2 from the second detection element 13 becomes stable around IV.

The exhaust gas recirculation amount setting routine will be explained with reference to FIG.

In step 1 (denoted as 31 in the figure; the same applies hereinafter), the intake air flow itQ detected by the air flow meter 23 and the engine rotation speed N detected by the crank angle sensor 33 are input.

In step 2, a basic fuel injection amount Tp (=-Q/N; is a constant) is calculated from the intake air flow rate Q and the engine speed N.

In step 3, the exhaust gas recirculation amount Eo corresponding to the engine speed N and basic fuel injection amount Tp at that time is searched from the preset MA knob.

In step 4, the electromotive voltage vl from the first detection element 12 is input.

In step 5, the electromotive voltage V2 from the second detection element 13 is input.

In step 6, the voltage difference ΔV (=V.

=■,) is calculated.

In step 7, the voltage difference ΔV is set to a predetermined value (for example, 200+s
V), if the value is less than the predetermined value, the steering knob 8
Then, the exhaust gas recirculation amount Eo retrieved in step 3 is substituted into the exhaust gas recirculation 31E.

If it is equal to or greater than the predetermined value, proceed to step knob 9, increase the exhaust gas recirculation amount Eo set in step 3 by, for example, 5 to 10%, and substitute it into the exhaust gas recirculation passage in step 10 (E4-
Eo (1+α), α is for example 0.05 or 0.1)
.

Here, step 8.10.11 corresponds to the exhaust gas recirculation amount control means, step 4.5.6.7 corresponds to the abnormality detection means, and step 9 corresponds to the change means.

After passing through step 8 or step 10, the routine proceeds to step 11, where the exhaust gas recirculation 31E is output to the control valve 32, and this routine ends.

As a result, due to changes in atmospheric pressure due to altitude, changes in combustion pressure, and deterioration of the orifice of the exhaust recirculation passage, the harmful component NOx remains in the exhaust gas after passing through the three-way catalyst. When there is a difference in the average electromotive force between the first detection element and the second detection element, an abnormality in the amount of NOx emissions is detected, the amount of exhaust gas recirculation is increased, and the combustion temperature is lowered.
It is possible to reduce NOx and make the three-way catalyst function effectively.

Furthermore, since only - number of diagnostic sensors 11 are required, the sensor installation space is also small, and the present invention can be implemented at low cost.

FIG. 9 shows another configuration of the diagnostic sensor. However, the same elements as those in the example shown in FIGS. 3 and 4 are given the same reference numerals, and the explanation thereof will be omitted.

That is, the first and second inner electrodes 15A of the first and second detection elements 12.13 are placed at opposing positions in the single atmosphere introduction chamber 19.
, 16A are provided, and the atmosphere introduction chamber 19 is shared by the first and second detection elements 12.13. The method of extracting the electromotive voltage is the same as in the previous example.

Even in such a configuration, the same functions as in the above-mentioned example can be obtained, and the sensor can be further miniaturized.

<Effects of the Invention> As explained above, according to the present invention, the amount of nitrogen oxide emissions in the exhaust gas can be reduced based on the electromotive force from the two detection elements of the diagnostic sensor provided downstream of the three-way catalyst. When an abnormality is detected, the amount of exhaust gas recirculated is increased to reduce the amount of nitrogen oxides emitted into the exhaust gas, allowing the three-way catalyst to function effectively.

Therefore, the effect of promoting purification of exhaust gas can be obtained.

[Brief explanation of drawings]

Fig. 1 is a functional block diagram showing the configuration of the present invention, Fig. 2 is a system diagram showing one embodiment, Fig. 3 is a diagram showing the structure of a diagnostic sensor according to the embodiment of the present invention, and Fig. 4 is the same as above. IV-
5 is a diagram showing the electromotive force characteristics of the same diagnostic sensor as above; FIGS. 6 and 7 are diagrams showing the output of the sensor; FIG. 8 is a flowchart showing control details; FIG. 9 is a diagram showing another embodiment of the diagnostic sensor. 11...Diagnostic sensor 12...First detection element
13...Second detection element 25...Fuel injection valve
26... Control unit 29... Air-fuel ratio sensor 31... Exhaust recirculation passage 32... Control valve 33... Crank angle sensor Patent holder Representative of Japan Electronics Co., Ltd.
Patent Attorney Fujio SasashimaFigure 2Figure 5Figure 4Figure 9

Claims (1)

[Scope of Claims] A three-way catalyst is provided in the exhaust passage of the engine, and an exhaust recirculation passage that recirculates part of the exhaust gas from upstream of the three-way catalyst to the intake passage; An exhaust gas purification device comprising: a control valve that controls a flow rate; and an exhaust recirculation amount control means that sets an exhaust recirculation amount based on the operating state of the engine and controls the exhaust recirculation amount via the control valve. Downstream of the main catalyst, there are two detection elements that are sensitive to oxygen and output an electromotive force according to the oxygen concentration. and an abnormality detection means for detecting an abnormality in nitrogen oxide emissions based on the difference in electromotive voltage between the two detection elements; An exhaust gas purification device for an internal combustion engine, comprising: a changing means for increasing the amount of exhaust gas recirculated by the exhaust gas recirculation amount control means upon detection.